Control means for railway train communication apparatus



May 12, 1942. w. P. PLACE CONTROL MEANS FOR RAILWAY TRAIN COMMUNICATION APPARATUS Filed July 19, 1940 ENTOR RPla'ce.

h v Nv QN MMML Il N ll/z'll H15 ATTORINEY Patented May 12, 19%2 CONTROL MEANS FOR RAILWAY TRAIN COMMUNICATION APPARATUS Willard 1'. Place, Wilkinsburg, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa. a corporation of Pennsylvania Application July 19, 1940, Serial No. 346,362

4.0laims.

Train communication systems using an inductor mounted on a vehicle of a train for inductively receiving energy from a wayside conductor to which communication current is supplied at some point remote from such vehicle are in use. One or both of the track rails are commonly employed as wayside conductors for transmitting such communication current and the inductor is mounted on the vehicle in inductive relation to the track rails. The communication current is usually a side band carrier telephone current. The train carried apparatus consists of one or more stages of high frequency amplification, the first stage of which is coupled to the inductor and the output side of the last stage of which is coupled to a demodulator. In the demodulator the telephone current is mixed with a local carrier current and the voice frequencies are filtered out and passed to a stage of low frequency amplification. The output side of this low frequency amplifier is connected to a telephone receiver or loud speaker so that the carrier telephone current picked up by the inductor is amplified and demodulated and the telephone message is reproduced at the loud speaker. In such communication apparatus earth current, stray magnetic fields, and other conditions may produce noise of a volume that may be annoying particularly during non-communication periods, since the receiving apparatus is normally conditioned for reception and because such apparatus provides a relatively high amplification. Furthermore, the energy level of the communication current may vary over a relatively wide range, because of the changing distance between the train and the sending station and because of other transmitting conditions.

In view of the foregoing conditions, a feature of my invention is the provision of novel and improved control means for railway train communication receiving apparatus wherewith the sensitivity of the receiving apparatus may be conditioned so that noise is substantially suppressed and the volume of the telephone message is substantially uniform throughout a relcontemplated for governing the sensitivity of receiving apparatus both manually and automatically, so that when noise energy is picked up and the operator believes the communication energy is substantially stronger than such noise energy, he may adjust the receiving apparatus to give the best response.

The above features, as well as other objects and advantages of my invention which will become apparent asthe specification progresses, I attain by an automatic control unit and a manually operable control unit. A condenser is connected to the output side of the last stage of amplification through a full wave rectifier so that a direct voltage proportional to the magnitude of the output of the amplifier is created across the terminals of the condenser. That is, the voltage created across the condenser is proportional to the magnitude of the energy picked up by the inductor. I also provide a local source of voltage consisting of a resistor connected across a source of direct current. A manually operable contact member adaptable of being set to engage different terminals connected to different taps of such resistor is provided so that the voltage between such contact member and a given terminal of the current source depends upon the position of the contact member. These two sources of voltage are connected to the grid of the electron tube of at least one high frequency amplifier in such a.manner that the sensitivity of the tube is controlled.

I shall describe two forms of apparatus em- 4 bodying my invention, and shall then point out atively large range of energy level of communication current.

A further feature of my invention is the provision of novel control means of the type here the novel features thereof in claims.

Referring to the drawing, Fig. 1 is a diagrammatic view showing one form of apparatus embodying my invention. Fig. 2 is a diagrammatic view showing a second form of apparatus also embodying my invention.

- In each of the two views like reference characters are used to designate similar parts.

Referring to Fig. 1, the receiving apparatus comprises an inductor, two stages of high frequency amplification, a demodulator, a low frequency stage of amplification and a telephone receiver. In Fig. l, the reference character 10 indicates an inductor mounted on a vehicle of a railway train in inductive relation to the track rails, not shown, the track rails being included in a transmitting circuit to which communication current is supplied at some remote point. It will be understood, of course, that a conductor other than the track rails may be used for transmitting the communication current, such con- A first and a second stage of high frequency amplification includes electron tubes VTI and VT2, respectively. As here shown, these electron tubes are of the indirect'heater cathode type, and their filaments are constantly heated in the usual manner. The inductor IC is connected across the primary winding 2 of an input transformer TI, the secondary winding 3 of which transformer is connected across thecontrol grid 4 and cathode 5 of tube VTI. A condenser 6 is preferably interposed between cathode 5 and the adjacent terminal of secondary winding 3 to complete the grid circuit for tube VTI. Plate voltage is supplied to tubes VTI and VT2 from a generator, not shown, but whose positive and negative terminals are indicated by the reference characters I B300 and N300, respectively. The plate circuit for tube VTI can be traced from terminal B300 of the current source through an inductor 8, resistor 3, a portion of winding |2 of a coupling transformer T2, plate 1 of tube VTI, intervening tube space to cathode 5, a resistor l3 and ground electrodes 4 and 50 to the negative terminal N300 of the current source. The winding '|2 of transformer T2 i coupled to the grid circuit for tube VT2 by the top terminal of winding 2 being connected to the control grid 5 of tube V'I2 through a condenser l6 and by the cathode I! of tube V'I'2 being' connected to a ground electrode l6 through a biasing unit IS. The plate circuit of tube VT2 comprises terminal B300, inductor 3, resistor 9, primary winding 20 of a coupling transformer T3, plate 2| of tube VT2, intervening tube space to cathode biasing unit l3 and ground electrodes l8 and 50-to terminal N300. The secondary winding 22 of transformer T3 is connected to the input side of a demodulator DM. It follows that electromo- 'tive forces picked up by inductor 10 are amplified at each of the two stages of amplification and are applied to the input side of demodulator DM. It will be understood, of course, that additional stages of amplification may be employed'if desired and also that one stage of amplification maybe omitted in the event the energy received by inductor IC is of a relatively high energy level.

The demodulator DM may take any one of several'well-known forms and is shown conventionally only for the sake of simplicity. It is sufiicient for this application to point out that when carrier telephone'current is applied to the demodulator it is mixed with a local carrier current and the voice frequencies are passed to the output side of the demodulator, the local carrier and the other products of demodulation being suppressed and filtered out. For example, the telephone current may be the upper side band of a carrier of 5700 cycles per second modulated with voice frequencies ranging from 400 to 2500 cycles per second so that the current transmitted is one having a frequency range of 6100 to 8200 cycles per second; In such case the amplified current of 6100 to 8200 cycles whenapplied to the demodulator DM is mixed with a local carrier of 5700 cycles and voice frequencies of 400 to 2500 cycles are supplied to the output side of the, demodulator, the carrier frequency and other frequencies resulting from demodulation being suppressed and filtered out. It will be understood of course that my invention is not rier current of such frequencies has been found satisfactory.

The output side of demodulator DM is connected over wires 23 and 24 to grid 25 and cathode 26 of a low frequency amplifier tube VT3, a

biasing unit 21 being interposed in the connection of wire 24 to cathode 26. The tube VT3, as here shown, is also of the indirectly heated cathode type and its filament is constantly heated 1 so that the tube is normally active. The plate circuit of tube VT3 includes terminal B300, primary winding 26 of an output transformer T4, plate 29 of tube VT3, intervening tube space to cathode 26, biasing unit 21 and ground electrodes 30 and to terminal N300 of the current source. One secondary winding 3| of output transformer T4 is connected to the operating winding of a telephone receiver or loud speaker LS. Hence the voice frequencies passed by demodulator DM are amplified by the low frequency amplifier and the resultant telephone message is reproduced at the loud speaker LS.

Another secondary winding 32 of output transformer T4 is connected to the input termnials of a full wave rectifier 33, the output terminals of which are connected to a. circuit including a condenser 0| 7 and a resistor 34 in multiple. It is clear that a direct voltage is created across condenser C I, the magnitude of which voltage is proportional to the electromotiv force induced in secondarywinding 32 due to the alternating current component of the plate circuit current of tube VT3. The connections are such that the polarity of the voltage created across condenser Cl is that indicated by the plus and minus signs in Fig. 1. The positive terminal of condenser Cl is connected to a ground electrode 35 and its negative terminal is connected over wire 31 to aterminal 36 to be referred to later. The resistor 34 is proportioned to discharge condenser C| during silent periods when no electromotive force is created in secondary winding 32 and resistor 34 may not be needed since the rectifier elements of rectifier 33 in their high resistance direction serve to discharge condenser Cl during such silent period. Consequently a voltage is created between ter-' minal 36 and ground electrode 35 proportional to themagnitude of the output energy of amplifier tube VT3.

A source of direct current such as a battery 5| is provided. The positive and negative terminals of battery 5| are indicated at B32 and N32, respectively. This source of direct current would preferably provided a voltage of the order of 32 volts and its positive terminal B32 is connected limited to the frequencies cited above but carto a ground electrode 31 so that the positive terminal B32 is in turn connected to the cathodes 5 and I! of the tubes VTI and VT2, respectively. through the ground electrodes I4 and 8. A resistor RC is connected across the terminals 332 and N32 of the direct current source and is provided with a series of taps connected to a corresponding series of terminals 38 to 4|, inclusive,

as will be clear by an inspection of Fig. 1. The terminals 33 to 4|, inclusive, together with terminal 36, are arranged so as to be engaged by a manually operable contact member 42 to form a voltage control unit the voltage of which is derived either from resistor RC or condenser Cl. Contact member 42 is constructed to pivot about a terminal 43, which terminal is connected'over wire 44 to the control grids 4 and I5 of tubes VTI and VT2,- respectively, the connection to control grid 4 being completed through a resistor R2 and secondary winding 3 of input transformer Tiyand the connection to control grid I! bein completed through a resistor RI.

As set forth earlier in the specification, the apparatus is normally conditioned for reception and to that end the filament of tubes VTI, VT2 and W3, as well as the filaments of the tubes included in demodulator DM are heated, and the generator which supplies power to terminals B300 and N31!!! is operated to supply a plate voltage to the several tubes. Under such normal conditions, and during silent periods when no communication energy is picked up by inductor IC, the loud speaker L8 is silent and no voltage is created across the condenser C I. If contact member 42 is set to engage terminal 36, then the negative bias voltage provided for the different tubes is that effected by the biasing unit interposed in the cathode connection of the different tubes and the apparatus is conditioned for relatively high gain due to the proportioning of the several parts. If the noise energy Picked up by inductor IC is low and contact member 42 is left in engagement with terminal 26, condenser Cl and its associated parts provide an automatic voltage control for the tubes VTI and VT2 according to the output energy of transformer T4. Also when telephone current is picked up by inductor IC, the control effected through condenser Cl is such that a high energy level for communication current increases the negative grid voltage applied to the high frequency amplifiers and reduces the sensitivity of the apparatus so that the response of the loud speaker is substantially uniform over a relatively wide range of telephone current energy. If conditions are such that noise energy is being picked up by inductor IC and the automatic control effected by condenser Cl is not suiiicient to suppress the noise at the loud speaker to a satisfactory degree, the contact member 42 may be set by the operator to engage one of the terminals 38 to 41, inclusive, to provide a negative grid voltage sufliciently high as to reduce the sensitivity of the apparatus to a point where the noise energy is a minimum, the maximum voltage being obtained when contact member 42 engages terminal 38 and the voltage progressively decreases to a minimum value when member 42 is set to engage terminal 4|. I have found that with the battery 5| of a voltage of the order of 32 volts, it is possible .to apply a high voltage bias to the amplifier tubes and render the receiving apparatus insensitive to a relatively large amount of noise energy received during silent periods of the telephone current. Also when the sending station is close and the telephone current energy high, the sensitivity of the apparatus can be reduced so that the telephone message is without distortion. This circuit arrangement at Fig. 1 would cause relatively little feed-back from the plate circuit to the grid circuit of each of the different high frequency amplifier tubes and distortion thereby would be avoided.

Referring to Fig. 2, the receiving apparatus comprises an inductor IC, two high frequency amplifier tubes VTI and VT2, a demodulator DM, a low frequency amplifier tube VT! and a loud speaker LS, the same as in Fig. 1, and a description of this part of the receiving apparatus need not be repeated. Also, condenser Ci of Fig. 2 is connected to a secondary winding 32 of output transformer T4, through full wave rectifier 33, the same as in Fig. 1. In Fig. 2, the negative terminal of condenser Cl is connected over wire 45 to the grids 4 and I! of tubes VTI and VT2, respectively, the connection to grid 4 being completed through resistor R2 and winding 2 f input transformer TI, and the connection to rid I5 being completed through resistor RI. \he positive terminal of condenser Cl is connected over wire 46 to the pivot terminal 42 of contact member 42, while contact member 42 is adapted to engage terminals 38 to 4|, inclusive, which are connected to resistor RC connected across battery ii, the same as in Fig. 1. In Fig. 2, the positive terminal B32 of battery 5| is connected to ground electrode 21, so that the positive terminal B32 is connected to the cathodes 5 and ll of the high frequency amplifier tubes, the same as in Fig. 1.

Normally the apparatus of Fig. 2 is conditioned for reception by the filaments of the tubes being heated and the plate voltage generator being normally operated. If contact member 42 is set to engage the terminal 4!, the positive terminal of condenser Cl is connected to ground electrode 31 through a minimum portion of resistor RC and the receiving apparatus is operated at full sensitivity with substantially only the automatic control created through condenser CI in effect. However, if conditions are such that an annoying amount of noise is present at the loud speaker the operator would move contact member 42' to the right to add a desired amount of .negative voltage from resistor RC and which voltage is superimposed on that developed across condenser Cl, with the result the sensitivity of the apparatus can be readily decreased to a point where the noise is substantially suppressed. That is to say, this negative voltage derived from the two control elements fixes the limi of the apparatus sensitivity so that noise weaker than a given limit is not heard. Telephone current energy now received operates to vary the voltage across condenser Cl so as to regulate the amplification gain automatically and the volume of the sound from the loud speaker is substantially uniform. Furthermore if the noise energy varies due to the train moving to a territory of either more or less noise energy, the operator can readily shift contact member 42 to adjust the sensitivity of the apparatus for best response in the new locality.

It is apparent that I have provided a novel control means by which train carried receiving apparatus of railway train communication systems can be conditioned to substantially suppress noise and to effect a substantially uniform vol. ume for the telephone conversation.

Although I have herein shown and described only two forms of control means for railway train communication apparatus, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In control means for use with railway train communication apparatus comprising an inductor mounted on a train for receiving carrier telephone energy, an electron tube amplifier having its control grid and cathode connected to such inductor and its output terminals connected to a demodulator to whose output side is coupled an output circuit adapted to actuate a telephone receiver; the combination comprising, a condenser coupled to said output circuit through a full wave rectifier to create a voltage across the terminals of said condenser proportional to the magnitude of the energy supplied to said'telephone receiver, a train carried source or direct current, a resistor connected across said direct current source and provided with a series of taps having diflerent voltages. said current source and said condenser each having its positive terminal connected to the cathode of said electron tube, a series of terminals a first one 01' which is connected to the negative terminal or said condenser and the others of which are connected one to each of the taps of said resistor, and a contact member connected to the control grid of said electron tube and adaptable of being set to engage any one of said series of terminals to control the sensitivity of such electron tube.

2. In control means for use with railway train communication apparatus comprising an inductor mounted on a train for receiving carrier telephone energy, an electron tube amplifier having its control grid and cathode connected to such inductor and its output terminals connected to a demodulator to whose output side is coupled an output circuit adapted to actuate a telephone receiver; the combination comprising, a condenser coupled to said output circuit through a full wave rectifier to create a voltage across the terminals of said condenser proportional to the magnitude of the energy supplied to said telephone receiver, a train vcarried source of direct current, a resistor connected across said current source and provided with taps, and means including a contact member adaptable of being set to engage any one of said resistor taps to serially connect said condenser and a selected portion of said resistor between the control grid and cathode of saidelectron tube to control the sensitivity of 'such tube to assure by the voltage derived from said condenser a substantially uniform predetermined energy level for said telephone receiver over a relatively wide variation of energy picked up by said inductor and to enable by the voltage derived from said resistor the energy supplied to the telephone receiver to here:- duced below said predetermined energy level when noise energy is picked up by the inductor.

3. In control means for use with railway train communication apparatus comprising an inductor mounted on 'a train for receiving carrier telephone energy, an electron tube amplifier having its control grid and cathode connected to such inductor and its output terminals connected to a demodulator to whose output side is coupled an output circuit adapted to actuate a telephone receiver; the combination comprising, a condenser coupled to said output circuit through a full wave rectifier to create a voltage across the terminals for that tube which is derived from the energy or said condenserproportional to the magnitude of the energy supplied to said telephone receiver,

a train carried source of direct current. a resistor connected across said current source and provided with taps, and means including another resistor and a contact member adaptable of being set'to engage any one of the taps of the first mentioned resistor to connect said condenser and a selected portion of said first mentioned resistor across the control grid and cathode of said electron tube to provide a'negative grid bias voltage supplied to said output circuit and the voltage drop in the selected portion of said first mentioned resistor whereby a substantially uniform predetermined energy level is assured for said telephone receiver over a relatively wide range of telephone energy picked up by said inductor bedemodulator to whose output side is coupled an output circuit adapted to supply energy to a telephone receiver; the combination comprising, a

condenser coupled to said output circuit through a rectifierto create across the terminals of said condenser a voltage proportional to the magnitude of the energy supplied to said output circuit, a train carried source of direct current, a resistor connected across said source and provided witha series of taps which have difierent voltages, a manually operable contact member capable of being set to engage any one of said taps, and circuit means including said condenser and said resistor connected across the grid and cathode of a biased grid voltage-which is effective to reduce a to a relatively low level the energy supplied to said telephone receiver when noise energy is picked up by said inductor.

WILLARD P. PLACE. 

